createDir failed for Windows because of recursion on absolute paths

This is a test (partly extracted from Aporia's code on suggest.nim for autocompletion).:

```nimrod
import os

proc getTempDir() : string =
  return os.getTempDir()

proc populateSuggest(): bool =
  var aporiaTmpDir = getTempDir() / "aporia"
  var prefixDir = aporiaTmpDir / "suggest"

  if not existsDir(aporiaTmpDir):
    createDir(prefixDir)

  if existsDir(prefixDir):
    removeDir(prefixDir)
  createDir(prefixDir)

discard populateSuggest()
```